I was responding more to the idea that they're discriminating against PhDs who've left academia. If it's not meant for anyone who's graduated, then it's discriminating equally against those who've stayed.

I was sort of kidding earlier. I tried registering with my current, academic, address and was rejected. I'm not surprised because it ends in "mx". The "joke" was that a PhD student at my university would have a similar looking email and I don't think they would have been accepted either. (I did have an "edu" when I was a student in the US and that address would probably have been accepted.)

You should ask a PhD student at your university to try. It'll be interesting if they get accepted.

It might not be too hard to cross-reference that email address against published papers to get an estimate of how long since you started the program, or even potentially find online records of your degree and/or thesis.